Some crude photometry has now been done. For comparisons 100 stars within 2 arcminutes of 2022qmx were searched in Gaia EDR3; their positions, G magnitudes and errors therein were saved. These and 2022qmx were analyzed with APT 2.8.2
The magnitude at JD 2459817.361, aka 2022-08-25 20:40 UT, is reported as 20.02 (0.02).
Crude, because my images were unfiltered but have been shown to be a decent match to Gaia G by and large.